1. Field of the Invention
The invention relates to a method of producing circuit structures and somewhat more particularly to producing layered structures consisting of silicides or silicide-polysilicon on substrates containing integrated semiconductor circuits by reactive sputter etching (ion etching) with sulfur hexafluoride as the etching gas and with the use of photosensitive resist etching masks.
2. Prior Art
Anisotropic etching techniques are used in etching technology for manufacture of fully integrated MOS circuits in order to insure a true-to-scale structure transfer. This type of anisotropic etching technique is described in Chemical Abstracts, Volume 85 (1976) Page 562, paragraphs 85:20 11 13 t and 85:20 11 14u. With these techniques, structures of a magnitude of 10 .mu.m are produced in polysilicon layers by reactive sputter etching with a mixture of gaseous oxygen and carbon tetrafluoride and with etching masks formed from films of photosensitive resist. In this process, the etching profile of the structures generated in the polysilicon layers is largely dependent on the thickness of the silicon layer and on the supplied high frequency power.
In order to reduce ohmic resistance of polysilicon lines in the manufacture of integrated circuits in MOS technology, the polysilicon lines are replaced by metal silicides or by applying an additional metal silicide layer (sometimes referred to as a "polycide" layer) on the polysilicon lines. In practicing this technique so as to be able to obtain generation of structures having a size in the range of 1 .mu.m, anisotropic etching techniques must be utilized. An anisotropic etching technique for a silicide in which CF.sub.4 is utilized as the etching gas is described in an article by B. L. Crowder et al, Transactions on Electron Devices, Vol. ED-26, (1979) pages 369-371. The described method is strictly anisotropic, however, because of its poor selectivity relative to the silicide, photosensitive resists cannot be utilized for the etching masks. Other masks, for example composed of aluminum, are possible but complicate the processing sequence. Yet a further disadvantage of this process is that the selectivity of polysilicon relative to SiO.sub.2 only amounts to approximately 2:1.
Published L. D. Forget et al European Patent Application No. 0015403 (1980) suggests that a further selectivity of polysilicon to SiO.sub.2 and Si.sub.3 N.sub.4 can be obtained by utilizing an etching gas mixture consisting of sulfur hexafluoride (SF.sub.6), chlorine and and inert gas in etching silicon substrates.